The overall quality of gases is of growing concern within semiconductor manufacturing facilities. In general, tremendous efforts are made to eliminate yield reducing contaminants from air used for semiconductor processing tools. For example, contaminants are viewed as molecular compounds present in a gas that can inhibit semiconductor processing tool performance through deposit formations. With lithography tools, gases are employed to purge and actuate tool components. Contaminants such as volatile silicon containing compounds in these gases are usually present at levels capable of damaging lithography tool optics.
Typically, volatile silicon containing compounds such as hexamethyldisiloxane and trimethylsilanol adhere to lithography tool optics, for example, projection lenses forming molecular films. These molecular films can physically absorb and scatter light, which distort wavefront qualities. When distorted, lithography tool images are abberated or misformed, preventing accurate circuit pattern formation onto a reticle. In addition to forming molecular films, contaminants can also degrade lithography tool optics. For example, hexamethyldisiloxane and trimethylsilanol can irreversibly degrade projection lenses, reducing fabrication yields.
Contaminants such as volatile silicon containing compounds hexamethyldisiloxane and trimethylsilanol pose particular concerns in microlithography tools. Other common lithography tool contaminants include acids such as hydrobromic acid, nitric acid, sulfuric acid, phosphoric acid or hydrochloric acid, bases such as tetramethylammonium hydroxide, ammonia, ammonium hydroxide, trimethylamine, methyl pyrrolidone, triethylamine, methylamine cyclohexylamine, ethanolamine, hexamethyldisilazane, dimethylamine, dimethylaminoethanol or morpholine, condensables such as hydrocarbons or silicones and dopants such as boric acid, organophosphate or arsenate.
The removal of hexamethyldisiloxane and trimethylsilanol from gases in semiconductor processing tools is often performed by filtering elements featuring intermixed chemisorptive and physisorptive medias. For example, such filter elements can include an acidic cation exchange resin intermixed with activated carbon. A filter element consisting of these chemisorptive and physisorptive medias can be mounted or coupled to a lithography tool. One shortcoming with filter elements having intermixed medias is that medias can exhaust at different rates, requiring less than optimal filter element replacements. Such different rates of exhaustion can also be exacerbated by varying concentrations and types of contaminants.